Twin sheet thermoformer

ABSTRACT

Apparatus and methods for fabricating a hollow plastic object from a pair of heat-fusible, thermoplastic sheets which are serially moved in a common horizontal plane from a heating station to a mold mechanism at a forming station. At the forming station, one of the sheets is received by a mold which is then moved vertically to move the sheet out of the plane to a position juxtaposed with a following sheet when the latter arrives at the forming station. At least one of the sheets is differential pressure molded after arrival at the forming station and the sheets are then vertically moved together and fused to form the object.

United States Patent 1191 Howell Feb. 25, 1975 [5 TWIN SHEETTHERMOFORMER 3,779,687 12/1973 A1551; 425/388 x 4 [75] Inventor: GeorgeH. Howell, Blrmmgham, 3 787 H1974 Brown et al 25/156 Mlch PrimaryExaminer-Robert L. Spicer, Jr. [73] Assignee: Koehring Company,Milwaukee, Attorney, Agent, or Firm-Learman & McCulloch Wis. 22 Filed:'Feb. 22, 1973. L d firi g? I h n l pparatus an met 0 s or a rtcatmg a oow p as- [211 Appl' 334,841 tic object from a pair of heat-fusible,thermoplastic sheets which are serially moved in a common horizon 521U.S. c1 425/504, 425/388, 425/162, tai Plane from heating Station to amold mechanism 425/157 425/1 0 425/403 2 4/92 425/453 at a formingstation. At the forming station, one of the [51] Int. Cl. B29c 17/04Sheets is received y a mold which is then moved 53 Field f Search 2 4 9297; 425 09 2 tically to move the sheet out of the plane to a position425/387, 157, 388, 160, 343, 408, 504, 453 juxtaposed with a followingsheet when the latter arrives at the forming station. At least one ofthe sheets 5 References Cited is differential pressure molded afterarrival at the UNITED STATES PATENTS forming station and the sheets arethen vertically moved together and fused to form the object. 3,256,5656/1966 Alest, Jr. et al 425/388 X 3,583,036 6/1971 Brown 425/388 x 6Claims, 9 Drawing Figures PATENTED FEB25I975 SHEEI 2 0F 8 TWIN SHEETTHERMOFORMER BACKGROUND or THE INVENTION 3,583,036, granted June 18,1971, includes sheet supporting carriages which support the sheets to bejoined in superposed relation as they move between a heating station anda forming station.

In another type of twin-sheet thermoforming machine, such as thatdisclosed in the present assignees copending patent application Ser. No.268,883, now U.S. Pat. No. 3,787,158, filed in the U.S. Patent Office onJuly 3, 1972, the plastic sheets are concurrently moved in oppositedirections and at different levels toward and away from a formingstation.

An object of the present invention is to provide a twin-sheet,differential pressure thermoforming machine wherein heat fusible,deformable, thermoplastic sheets may be successively delivered in acommon plane path to a forming station where a configuration is moldedin at least one of the sheets and the sheets are thereafter fusedtogether to form an object.

Another object of the present invention is to provide twin-sheetthermoforming apparatus of the character described which includes asheet supply system for serially supplying deformable, synthetic plasticsheets in a common plane circuit to the forming station.

Still another object of the present invention is to provide differentialpressure, twin-sheet thermoforming apparatus having a load-unloadstation at which a pair of sheets used to form an object aresuccessively loaded on carriages successively moving past the station,and at which an object formed in the sheets is subsequently removed fromone of the carriages at the load-unload station.

Another object of the present invention is to provide double-sheet,differential pressure forming methods and apparatus for successivelymoving deformable sheets to a forming station, then moving one of thesheets out of the path of travel to a position juxtaposed with afollowing sheet when it is moved to the forming station, and then fusingthe sheets together to form the object.

Machines of the type disclosed in the aforementioned patent and patentapplication are capable of forming objects in pairs of plastic sheets ofdiffering thicknesses. The thicker sheets must be subjected to heat,from a given heating source, for a longer period of time than thethinner sheets. If the thinner sheets are subjected to the same heat asthat required to prepare the thicker sheets, the thinner sheets willlose their strength and excessively sag. In the apparatus disclosed inthe referenced patent, the upper and lower sheets must be maintained atthe heating station for the same length of time. Thus, the heating ofone sheet is always related to the heating of another sheet. It is afurther object of the present invention to provide double-sheetdifferential pressure forming apparatus for serially moving sheets froma heating station to a forming station and heating the sheetsindependently of each other.

Other objects and advantages of the present invention will becomeapparent to those of ordinary skill in the art as the descriptionthereof proceeds.

SUMMARY OF THE INVENTION Apparatus for fabricating a hollow object froma pair of deformable, thermoplastic sheets comprising: frame means witha heating station and a forming station downstream of the heatingstation; carrier means for serially moving first and second deformable,thermoplastic sheets from the heating station to the forming station;means for heating the first and second sheets at the heating station;and means for moving the first sheet away from the carrier means whenthe first sheet is at the forming station to a position in which it willbe juxtaposed with the second sheet when the latter is moved to theforming station, for applying a differential pressure to opposite sidesof at least one of the sheets to form a shape therein, and for clampingthe juxtaposed sheets together to fuse the sheets and form the object.

The present invention may more readily be understood by reference to theaccompanying drawings, in which:

FIG. 1 is a top plan view of a rotary thermoforming machine constructedaccording to the present invention, part of the sheet heating apparatusbeing broken away to illustrate the underlying carriage;

FIG. 2 is a partly sectional, front elevational view, taken on the line2-2 of FIG. 1, part of the machine being broken away to more clearlyillustrate a portion of the sheet heating apparatus;

FIG. 3 is a transverse sectional view, taken on the line 33 of FIG. 1;

FIG. 4 is an enlarged, vertical sectional view, taken on the line 44 ofFIG. I, particularly illustrating an upper mold in a raised removedposition and a lower mold in a raised sheet-engaging position, forming ashape in a sheet at the forming station;

FIG. 4A is a fragmentary top plan view of a platen locking cylinder,taken along the line 4A-4A of FIG.

FIG. 5 is a view similar to FIG. 4, showing the lower mold carrying apreviously molded sheet in a lowered dwell position and the upper moldin a lowered forming position, molding a shape in another sheet ofplastic which has been subsequently indexed to the forming station;

FIG. 6 is an enlarged vertical, sectional view similar to FIG. 5,illustrating the upper and lower molds in closed position, the lowermold being illustrated in a position elevated with respect to the lowermold support platen, in which the upper and lower sheets are fusedtogether; and i 1 FIGS. 7 and 7A, taken together, comprise a schematicdiagram of a typical electrical control circuit for controlling theoperation of the various elements of the machine illustrated in FIGS.16.

Referring now more particularly to the accompanying drawings, and in thefirst instance particularly to FIG. 1, a rotary plastic sheet supportingcarrier or turntable C is mounted for rotary, indexing movement on afragmentarily illustrated, stationary frame F by a central shaft 10journaled in the frame F in the usual manner. The turntable C includes acircular, spoked disc F having radial spokes 10a fixed to the centralshaft 10 and mounting an annular rim 10b. The turntable C mounts fourcircuitously arranged sheet supporting, clamp frame assemblies,generally designated 16, for gripping the edges of deformable webs orsheets of synthetic plastic, thermoplastic sheets P1, P2, P3 and P4which may be on the order of 36 to 48 inches in size. The sheets P2 andP4 are lighter gauge sheets which typically may be 0.200 inches thick,and the sheets P1 and P3 are heavier gauge material, on the order of,for example, 0.250 inches in thickness. The clamp frame assemblies,generally designated 16, are of the same character as the clamp frameassemblies disclosed in the aforementioned patent except that they areused in inverted position, and they each clamp a single sheet or web ofsynthetic plastic material instead of a pair of such sheets. The clampframe assembly 16 will not be described in detail in view of their fulldisclosure in the aforementioned patent. As usual, however, theycomprise a pair of juxtaposed frames 23 and 24 (see FIG. 4). Each of theframes 24 is made up of four separate sections in rectangular formationwhich are pivotally mounted to swing downwardly and outwardly to releasethe plastic sheet held therein upon retraction of the piston rods 25 ofa plurality of conventional, double acting, fluid pressure operatedclamp cylinders 26.

Suitable synthetic plastic sheets which may be thermoformed in a mannerto be described, are polystyrene, polyethylene and polypropylene, but itis contemplated that various thermoplastic materials may be thermoformedin the manner indicated and then assembled to form parts which consistof upper and lower sheets thermoformed to desired configurations. Theapparatus constructed according to the present invention is particularlyuseful for forming large size containers of various types in variousindustries, such as holding tanks for the recreational vehicle industry,and may be also used to form such diverse products as hollow, plasticshutters and pallets.

Provided on the frame F is a loading-unloading station, generallydesignated 11, first and second sheet heating stations, generallydesignated 12 and 13, and a forming and assembly station, generallydesignated 14. A frame supported, double acting, solenoid actuated,spring returned, cylinder 9 is provided for indexing the turntable C tosuccessively move the sheets P1 P4 to the various stations. The clampedsheets Pl P4 are successively incrementally indexed by the turntable Cfrom the loading-unloading station, generally desig nated 11, betweenvertically spaced banks of heaters and 15a at the first and second sheetheating stations 12 and 13, respectively, and then to a position betweenupper and lower molds l9 and at the forming station 14. Conventionalgeneva or other apparatus couples the piston rod 9' of cylinder 9 to theturntable disc shaft 10 to index the turntable 90 each time the pistonrod is extended.

At the loading-unloading station 11, a sheet supply carrier or table 27is actuated by the piston rod 28 of a conventional single-acting,solenoid actuated, spring returned fluid pressure operated cylinder 29for vertical movement between a lowered, sheet receiving position and araised, sheet discharging position adjacent a sheet clamp frame assembly16. Frame supported, vertically disposed sheet guide rods 30 areprovided so that the plastic sheet becomes automatically centered inproper position on the table 27 when the table 27 is in lowered positionbeneath the level of the guides 30 and the operator places the plasticsheet thereon.

In FIG. 2, the frame clamp bars 24 are shown swung to a plasticsheet'releasing position so as to receive the sheet P1 which is beingraised. into position to be clamped by the clamp frame 16 at theloadingunloading station 11 (see FIG. 2). The operator alternatelysupplies sheets of thin and heavier gauge, for example, on the other of0.200 thousandths and 0.250 thousandths, respectively, for a purposewhich will later become apparent. When the table 27 is raised to itsuppermost position in which the plastic sheet engages the upper framepart 23 of the clamp frame assembly 16, a limit switch LS-12 is trippedand the cylinders 26 are actuated to pivot the clamp frame elements 24and clamp the sheet Pl between upper and lower frame parts 23 and 24,respectively, in the manner indicated in FIG. 4.

At the heating station 12, conventional resistance type, elongateheating elements 15 are supported on the frame F by frame structure 17and 18 above and below the rotary path of the four clamp frameassemblies 16. The heater elements 15 comprise quartz tubes of the typemanufactured by E. L. Weigand Company of New Jersey, or General ElectricCompany. The quartz heaters 15 are flashed for a very short period,i.e., 10 seconds, when the thin sheets P2 and P4 are at the firstheating station 12 and are maintained energized for a longer period whenthicker sheets P1 and P3 are at the first heating station 12. At theheating station 13, conventional infra-red type, elongate heatingelements 15a are supported on the frame F by frame structure 17a and18a. The infra-red heaters 15a are intermittently operated for a portionof the total time the sheets are at the second heating station 13.

At the forming station 14, upper and lower mold members 19 and 20,respectively (see FIG. 4), are mounted so as to be vertically moved byconventional, double acting, fluid pressure operated cylinders 21 and22, respectively. The lower mold raising cylinder 22 is solenoidactuated on both the upstroke and return, but the upper mold loweringcylinder 21 is solenoid actuated to the extend position and is springreturned to the retracted or raised position.

As FIGS. 4 and 5 both particularly indicate, the upper and lower molds19 and 20 are provided with vacuum manifolds 31 and 32, respectively,which communicate respectively with vacuum source lines 33 and 34. Themold cavities 35 and 36 of molds 19 and 20, respectively, are providedwith ports 37 communicating with the manifolds 31 and 32, respectively.As particularly indicated in FIG. 4, the upper mold 19 is s'upported onan upper platen, generally designated 38, which includes side rails 38e,spanned by platen brace rods 38c and channel plate 38b. The channelplates 38b are sandwiched between a mold plate 38a, fixed to the uppermold 19, and a mold plate 38d fixed to the piston rod 21a ofthe cylinder21. The upper platen 38 mounts guide rods 39 that are received incushioning cylinders 40 secured to the frame structure F. The upperplaten 38 supports fixed nuts 42, which threadedly receive lock shafts43, having locking lugs 44 at their lower ends. As FIG. I particularlyindicates, four such lock shafts 43 are provided and are revolved inunison by collars 45 which are fixed thereto to achieve a lockingoperation in a manner which will be described.

A pair of lugs or ears 46 and 47 (FIG. 1) are fixed to each collar 45. Asolenoid controlled, double acting, fluid pressure operated cylinder 48is provided on the upper platen 38 for rotating the vertical platenlocking shafts 43 in unison via a linkage system including a link 49pivotally connected at its ends to the ears 47 of the collars 45 at theright end of the assembly in FIG. 1, and a link 50 pivotally connectedat its ends to the-ears 46 of the radially outermost collars 45.Finally, a link 51 is also pivotally connected at its ends to the ears47 on the collars 45 at the left end of the mold station as viewed inFIG. 1.

As FIG. 4 also indicates, the lower mold 20 is supported by a lowerplaten, generally designated 52, which includes side frame members 53,spanned by brace rods 53c, supporting fixed nuts 53a that receivevertical, threaded rods 54 having heads 55 provided with key-holeopenings 55a for receiving the platen locking shafts 43 and lugs 44. Theinner ends of the key-hole openings include offset portions 55b (FIG. 4)which receive the lugs 44 when the lock shafts 43 are revolved 90 tolock the platens together.

The lower platen 52 includes a cross bar 52fmounted on the piston rod22a of the lower hydraulically operated cylinder 22 and carries guiderods 56 which are received in cushioning cylinders 40 fixed to the framestructure F. Spanning the side rails 53 of the lower platen 52 is alower pressure plate 57 which, at its four corners, mounts verticalguide rods or pins 58 which are freely and slidably received in openings59 provided in an upper pressure plate 60. The upper pressure plate 60is connected to the underside of the lower mold 20 via channel plates 61and a manifold plate 62.

Apparatus is provided for moving the lower mold 20 upwardly relative tothe lower platen 52, when the sheets are clamped between the molds 19and 20, and includes a series of individual hose-like, air-expansiblebladders 63, provided between the relatively movable pressure plates 57and 60. Plainly, when air is admitted to the bladders 63, the pressureplate 60 and lower mold -20 will immediately be forced upwardly to pinchthe upper and lower sheets clamped between the molds 19 and 20 at theforming station to a single sheet thickness (see FIG. 6). It is to beunderstood that the bladders 63 are formed of a flexible, collapsiblematerial such as a resilient fabric, which normally is in thesemicollapsed condition shown in FIG. 4. Rigid end plates 63a areprovided for the inflatable tubes 63 and their air pressure supply tubes64 lead into one end of each expansible tube 63 through a rigid endplate 63a, as shown in FIG. 3. Individual valves 65 for the tubes 64permit each of the tubes 63 to be shut down, if desired, when they arenot necessary to the mold raising operation and there is no need for airfrom a manifold 66 to be communicated to them via their supply tube 64.

To insure that the sheet supporting carriages 16 are halted in theidentical position at the forming station each time the turntable C isindexed, apparatus for locking the turntable C in the various fullyindexed position is provided and comprises a rim lock 70 pivotallymounted on a frame supported shaft 72 for movement between the unlockedposition, illustrated in FIG. 1, and a rim engaging position received inany one of a plurality of recesses 77 provided in the rim b of theturntable C. To swing the lock 70, a solenoid actuated, spring returned,fluid pressure operated control cylinder 74 is provided including apiston rod 75 coupled to the pivoted rim lock 70. A limit switch LS-9 istripped by the rim lock 70 in the unlocked position.

A plurality of limit switches are provided for controlling the operationof the machine and include a pair of limit switches LS-3 and LS-4mounted apart on the frame F in position to be alternately tripped by apair of 180 spaced paddles 76 fixed to the turntable shaft 10.

The upper mold 19 includes a molding pressure needle 84 which is movablethrough an aperture 840 in the mold sidewall to pierce a sheet ofplastic drawn into the upper mold cavity 35 and introduce pressurizedair into the deformed sheet for assisting it into intimate conformitywith the upper mold cavity 35.

Top and bottom platen extend" limit switches LS-5 and LS-6 (FIG. 4) aresupported on the frame to be tripped by the upper and lower molds l9 and20, respeetively, in their closed molding positions, illustrated in FIG.3. A platen lock" limit switch LS-7 is mounted on the upper platen 38 tobe tripped when the lock 44 moves to platen locking position. A rim lockopen" limit switch LS-9 is mounted on the frame F in position to betripped when the rim lock 70 is retracted from the rim 10b. A platenunlock limit switch LS-10 is mounted on the upper plate 38 in positionto be tripped when the platen locks 44 move to a platen unlockingposition aligned with the key-hole 55b in the head 55 supported on thelower platen 53.

A bottom platen extend" limit switch LS-ll (FIG. 4) is mounted on theframe F in position to be tripped when the bottom mold 20 is moved tothe molding position illustrated in FIG. 3. A load table extend" limitswitch LS-l2 is mounted on the frame F at the load station 11 inposition to be tripped when the sheet supply or load table 27 isextended from the position illustrated in FIG. 2 to a raised position ata clamp frame assembly 16.

A plurality of clamp frame limit switches LS-17, LS-18, LS-19 and LS-20are supported on the turntable C in position to be tripped when thesheets P1 P4, respeetively, reach the forming station 14. Apparatus fortripping the limit switches LS-17 through LS-20 comprises a cylinder 91,at the forming station 14, having a piston rod 92 which extends into thepath of the limit switches LS-17 and LS-20. The limit switches LS-l7through LS-20 are also successively tripped at the loadunload station 11by the piston rod 94 of a double acting, solenoid actuated, fluidpressure operated cylinder 93 which is selectively energized. A sheetsupply control limit switch LS-2l is mounted in the turntable C inposition to be tripped when the frame 16 opens at. the load-unloadstation.

THE CONTROL CIRCUIT The control circuit for controlling the apparatuspreviously described is schematically illustrated in FIGS. 7 and 7A, andincludes a pair of electrical supply lines L1 and L2 connected across asupply of electrical power such as volt, 60 cycle, alternating currentand a plurality of circuit and sub-circuit lines designated L3 throughL37, respectively. Connected in line L3 across the lines L1 and L2 arethe normally open relay contacts 5CR1, which are closed when a relay SCR(line L5) is energized, and a control relay 3CR which, when energized,opens a pair of normally closed contacts 3CR1 (Line L26) and closes apair of normally open contacts 3CR2 (line L28). Connected in Line L4across the lines L1 and L2 are the normally closed limit switch contactsLS-3a which are opened when the frame supported limit switch LS-3 istripped by a paddle 76 on the turntable shaft 10, as is illustrated inFlG. 4. Connected in series with the limit switch contacts LS-3a (lineL4) are the normally open timer contacts T1A which close as a timer T1(line L8) times out, and a rim lock solenoid 74a for moving the pistonrod 75 of the rim lock cylinder74 in such a manner as to move the rimlock 75 to locking position in one of the recesses 77 in the turntablerim 10b. The junction 80a (line L3) of the timer contacts T1A and therim lock solenoid 74a is also connected to the control relay 3CR via aline 80. Connected in line L5, across the lines L1 and L2, is a set ofnormally closed limit switch contacts LS-4a which are opened and closedalternately with the contacts LS-3a by the turntable supported paddles76. Also serially connected in line L5 is a set of normally open timercontacts T4A which close as a timer T4 (line L) times out, and a holdingrelay SCR which, when energized, is operative to close the normally opencontacts 5CR1 (line L3).

Connected between the junction 81 (line L4) of limit switch contactsLS-3a and timer contacts TIA (line L4) and the line L2 is a plurality ofparallel circuits including lines L6, L8, L9, L9A and line L10A. Line L6includes the normally open timer contacts TlB which close as the timerT1 (line L8) times out and the normally open limit switch contactsLS-5a, which close when the frame supported limit switch LS-5 is trippedby the upper mold 19 in the fully extended, molding position at thesheet line. Also connected in line L6 is a set of normally open limitswitch contacts LS-6a which are closed when the frame supported limitswitch LS-6 is tripped by the lower mold in the fully extended positionat the sheet line, as is illustrated in FIG. 3. The line L6 alsoincludes the platen lock control solenoid 48a which, when energized,actuates the platen lock control cylinder 48 in such a manner as torotate the platen lock shafts 43 above their axes to lock the platens 38and 52 together. Connected in parallel with the platen lock solenoid 48ais a holding relay lTDR (line L6A) which, when energized, closes a setof normally open holding contacts lTDRl (line L22).

Connected in line L7 between the junction 82 (line L6) of timer contactsTlB and limit switch contacts LS-Sa (line L6) and the line L2 is a setof normally open limit switch contacts LS-7a which close when the upperplaten supported limit switch LS-7 is tripped by the lock shafts 43 andlocking lugs 44 moving to the platen locking positions. Connected inseries with the limit switch contacts LS-7a (line L7) are the normallyopen timer contacts TlC which close as the timer T1 (line L8) times out,and a sheet pinching" solenoid 65a or operating the valve which suppliespressurized air via the tube 66 to the air expansible bellows orbladders 63. This forces the lower mold 20 upwardly, relative to thelower platen 52, toward the mold 19 to pinch the double thickness sheetsand provide a single thickness perimetrical portion on the containerformed at the forming station 14.

A solenoid 84a (line L7A) for moving the air pressure supplying needle84 through the sheet in the upper mold and admitting mold pressurethereto is connected in parallel with the solenoid 65a. A pressureresponsive switch 86 is connected in series with the solenoid 84 and isset at a pressure of p.s.i., for example, which will interrupt moldpressure and withdraw the needle 8 when the predetermined pressure isreached in the upper mold cavity 35.

Connected in lines L8 and L9 are the vacuum control timer T1 andpressure forming control timer T2, respectively. The timer T1, whenenergized, sequentially closes the timer contacts TlA (line L4), T1B(line L6), TIC (line L7), TlD (line L11), TIE (line L12). The timer T2,when energized, sequentially closes the normally open timer contacts T2A(line L23), T2B (line L25), and T2C (line L26). The specific sequence oftimer contact closing will be more particularly described hereinafter.Connected in line 9A between the junction 81 and line L2 is a timer T9including normally open timer contacts T9A (line L14) which close as thetimer T9 times out. Also connected between the junction 81 (line L4) andthe line L2 is a timcr T10 (line L10A) which closes the normally opentimer contacts T10A (line L16) as it times out.

Connected between the junction 87 (line L5) of the normally closed limitswitch contacts LS-4a (line L5) and timer contacts T4A and line L2 is acircuit line L10, including a timer T4 which sequentially closes thenormally open timer contacts T4A (line L5), T4B (line L13), T4C (lineL15), T4D (line L17), T4B (line L24), T4F (line L27) and T46 (line L29).The sequence of timer contact closing will be more particularlydescribed hereinafter.

Connected in line L11, across the lines L1 and L2, are the normally opentimer contacts T1D and a vacuum control solenoid 33A for communicatingforming vacuum to the upper mold 19. Connected in line L12, across thelines L1 and L2, are the normally open timer contacts TIE and the lowervacuum control solenoid 34a for introducing forming vacuum to the lowermold 20.

Connected in line L13, in parallel with the timer contacts TIE, are thenormally open timer contacts T4B. Connected in line L14, across thelines L1 and L2, are the normally closed, manually operated, toggleswitch TS-l, the normally open timer contacts T9A, which close as thetimer T9 (line L9A) times out, and a top heater control relay lCR which,when energized, operates the top heaters 15 at the first heating station12. Connected in parallel with the timer contacts T9A (line L14) are thetimer contacts T4C which close as the timer T4 times out to energize thecontrol relay lCR (line L14). The timer contacts T4C remain closed for ashorter period of time than do contacts T9A as will be later described.The circuit line 16 is connected across the lines L1 and L2 and includesthe control circuitry for the bottom heaters 15 at the first heaterstation or oven 12. Connected in line L16 is a set of normally closed,toggle switch contacts TS-2, the normally open timer contacts T10A whichclose as the timer T10 times out, and the oven control relay 2CR which,when energized, causes the bottom quartz heaters 15 at the first heatingstation 11 to be energized. Connected in line L17 in parallel with thetimer contacts T10A is a set of timer contacts T4D (line L17) which areclosed as the timer T4 times out.

The control circuitry for controlling the top infra-red heaters 15A atthe second heating station or oven 13 is connected in line L18, acrossthe lines L1 and L2, and comprises a normally closed, manually operated,toggle switch TS-3 and a timer T7 which opens a set of normally closedtimer contacts T7A (line L19) as the timer T7 times out. Line L19 isconnected in parallel with timer T7 and includes the timer contacts T7Aconnected in series with a bottom heater oven control relay 3C0. Whenthe relay 3C0 (line L19) is energized, the top infra-red heatingelements 15A at the second heating station 13 or oven are energized.

The control circuitry for the bottom heating elements 15a at the secondheating station or oven 13 is connected in line L20 across the lines L1and L2 and comprises a set of normally closed, manually operated toggleswitch contacts TS-4 and a timer T8 including a set of normally closedcontacts T8A (line L21) which open as the timer T8 times out. Thecircuit line L21 is connected in parallel with the timer T8 and includesthe timer contacts T8 connected in series with a control relay 4CR forenergizing the bottom heater elements 15A. The timers T1, T2, T3, T4,T5, T6, T9 and T10 are multiple station, settable, linear timers of thetype manufactured by Eagle Manufacturing Company as Model No.HM5-05-A6-02-06 and include separably energized clutches (not shown) asusual. The timers T7 and T8 are also multiple station, linear timers ofthe same general type, but are settable to intermittently open and closethe contacts T7A and T8A for a percentage of the total running time ofthe timer motors. For example, the timers T7 and T8 typically operatefor 120 seconds, but the contacts T7A might only be closed for 108seconds or 90 percent of the total timing period.

Circuit line L23 is connected across the lines Ll an L2 and includes thecontrol circuitry for lowering the upper mold 19 to the sheet lineposition and comprises a set of normally closed limit switch contactsLS-9a, which is opened when the rim lock 70 is in the unlocked positionto actuate the limit switch LS-9, the normally open timer contacts T2A,which close as the forming timer T2 times out, and an upper moldlowering solenoid 210 which, when energized, directs fluid to thecylinder 21 in such a direction as to move the upper mold 19 to themolding position engaging a sheet on one of the carriages 16. Connectedbetween the junction of the timer contacts T2A (line L23) and the uppermold lowering solenoid 21a and the line L1 is a circuit line L22including the normally open holding contacts lTDRl which are closed whenthe holding relay lTDR (line L6A) is closed.

Connected between a junction 90 (line L23) of the limit switch contactsLS-9a and the timer contacts T2A and the line L2 are circuit lines L25and L26. Circuit line L25 includes the control circuitry for raising thelower mold 20 and comprises the normally open timer contacts T2B whichclose as the forming timer T2 (line L9) times out, after a shape ismolded in one of the thicker sheets, and a solenoid 22a for moving thelower mold 20 upwardly to the mold position illustrated in FIG. 3.Connected in parallel with the timer contacts T2B (line L25) is a set oftimer contacts T4E (line L24) which close as the timer T4 (line L10)times out after a shape is molded in one of the thinner sheets.

The circuit for retracting the lower mold 19 is connected in the circuitline L26, across the lines L1 and L2 and includes the normally closedrelay contacts 3CR1, which are opened when the relay 3CR (line L3) isenergized, the normally open timer contacts T2C which close as thethicker sheet, forming timer T2 times out, the normally closed limitswitch contacts LS- lu, which are closed as the platen locks 44 areunlocked to trip the limit switch LS-10, and the lowering solenoid 22bfor directing fluid to the cylinder 22 to move the lower mold 20 to thelowered position illustrated in FIG. 5. Connected in line L27, inparallel with the contacts 3CR1 and T2C (line L26), is the set of timercontacts T4F which are closed as the thin sheet timer T4 times out. Aswill be described more particularly hereinafter, the timer contacts T4Eand T4F for the thin sheet timer T4 are closed for a substantiallyshorter period than the timer contacts TZB and T2C for the thick sheettimer T2 so that the lower mold 20 will dwell at the sheet line positionfor a longer period when a thick sheet is being formed. Connectedbetween the line L1 and the junction of the timer contacts TZC (lineL25) and the limit switch contacts LS-a is a set of normally openholding contacts 3CR2 which close when the holding relay 3CR (line L3)is energized.

The control circuit for energizing the turntable indexing cylinder 9 isconnected in line L9, across the lines L1 and L2, and includes a set ofnormally open limit switchcontacts LS-9a which close when the rim lock70 is unlocked to trip the limit switch LS-9, and a solenoid 9A fordirecting fluid to the turntable indexing cylinder 9, to rapidlyaccelerate the turntable C. A line L33 is connected across the solenoid9A and includes the normally open limit switch contacts LS-l6a, whichclose when a frame supported limit switch LS-l6 is tripped midwaythrough the stroke of the piston rod 9, and a solenoid R which, whenenergized, interrupts the supply of air to the cylinder 9 so that thepiston rod 9 is permitted to coast to its fully extended position sothat the turntable is not abruptly halted at the end of the piston rodstroke.

A pair of conventional current carrying brushes, schematicallydesignated 94 and 95 (FIG. 7) are connected to the lines L1 and L2respectively, and engage a pair of slip rings, schematically designated96 and 97 respectively, connected to a pair of circuit lines L1 and L2on the turntable C.

Connected across the lines L1 and L2 are circuit lines L34 L37 forcontrolling the opening and closing of the clamp frame assemblies 16supporting the sheets P1 P4. Connected in the circuit line L34, are aset of normally open limit switch contacts LS-l7u, which close when theturntable supported limit switch LS-17 is tripped, and a solenoid 26Awhich actuates the solenoid actuated, spring returned, clamping framecylinders 26 on the carriage 16 carrying the sheet P4 to release thesheet P4. 50 Connected in line L35 is a set of normally open limitswitch contacts LS-l8a which close when the turntable supported limitswitch LS-l8 is tripped, and a solenoid 268 which energizes the clampingframe solenoids 26 to retract the frame members 24 and 25 gripping thesheet P3 and release the sheet P3. Connected in line L36 is a set ofnormally open limit switch contacts LS- 19a, which close when theturntable supported limit switch LS-l9 is tripped, and the solenoid 26Cfor energizing the solenoid actuated, spring returned, clamp framecylinders 26 on the carriage which supports the sheet P2 to release thesheet P2. Connected in line L37 is a set of limit switch contacts LS-a,which are closed when the turntable supported limit switch LS-20 istripped, and a solenoid 26D which, when energized, retracts the clampingframe members 24 and which support the sheet P1 to release the sheet.

Circuit lines L29, L30, and L31 are connected in parallel across theline L1 and L2 and control the actuation of the limit switches LS-l7through LS-20 at the forming and load-unload stations as will presentlybe described. A solenoid actuated, spring returned, fluid operatedcylinder 91 is mounted on the frame F at the forming station 14 andincludes a piston rod 92 which is extendable to trip the turntablesupported limit switches LS-l7 and LS-l9 to release the thin sheets P2 Iand P4 at the forming station'after a shape is formed therein. A doubleacting, solenoid controlled, fluid pressure operated cylinder 93 ismounted on the frame F at the load-unload station 11 and includes'apiston rod 94 extendable to trip the turntable supported limit switchesLS-l7 through LS-20 at the load-unload station 11. This will open theclamp frame assemblies 16 to release sheets having objects formedtherein and prepare the carriage clamp frame assemblies 16 to receiveother sheets.

Circuit line L29 includes the normally open timer contact T4G, a set ofnormally open limit switch contacts LS-l la, which close when a limitswitch LS-ll at the forming station 14 is tripped by the lower mold 20at the forming position, and a solenoid 910 which, when actuated, causesthe piston rod 92 of the cylinder 91 to be extended.

Connected in line L30 is a set of normally open limit switch contactsLS-13a, which close when the upper mold 19 extends to mold position totrip the frame supported limit switch LS-l3 at the forming station 14,the normally closed limit switch contacts 93b1, which open when asolenoid 93b (line L31) is energized, and a clamp frame opening solenoid93a for extending the piston rod 94 of the cylinder 93. Connected inline L31 is a set of normally open limit switch contacts LS-12a of alimit switch LS-12, which is tripped when the load table 27 is upwardlyextended at the sheet load-unload station 11, and the clamp frame closesolenoid 93b for retracting the piston rod 94 of cylinder 93 so that theclamp frame assemblies can be closed at the loadunload station 11.

Circuit line L33A includes a set of normally open limit switch contactsLS-21a, which are closed when a frame supported limit switch is trippedby the frame assemblies 16 opening at the load-unload station 11,connected in series with a solenoid 29a which, when energized, actuatesthe solenoid actuated, spring returned, fluid pressure operated sheetsupply table raising cylinder 29.

THE OPERATION It will be assumed that the machine is in the midst of itscontinuous cycle and a sheet PI is clamped in the clamp frame 16 at theloading-unloading station 11, a sheet P2 is clamped in the clamp frameassembly 16 between the heaters 15 at the oven or heating station 12, asheet P3 is clamped in a sheet clamp frame assembly 16 at the oven orheating station 13, and a sheet P4 is clamped in a sheet clamp frame 16at the forming station 14.

Shapes are molded in the lighter gauge sheets P4 and P2 by the lowermold 20, and the shapes are molded in the heavier gauge sheets P1 and P3by the upper mold 19 as will presently be described. At the time thesheet P4 is initially delivered to the forming station 14, the upper andlower molds 19 and 20 are in the spread, chain line positions,illustrated in FIG. 2. The limit switch LS-3 will have been actuated byone of the paddles 76, as illustrated in FIG. 1, to open the limitswitch contacts LS-3a (line L4) while the limit switch contacts LS-4a(line L5) remain closed to energize the timer T4 (line L10 As the timerT4 times out, the contacts T4E (line L24) will close to energize thelower platen raising solenoid 22a (line L25) for raising the lowerplaten 52 and lower mold 20 upwardly to the sheet line position,illustrated in FIG. 4, engaging the sheet P4.

The timer contacts T4B (line L13) are set to close at the time the mold20 engages the sheet P4 to energize the solenoid 34a (line L12) whichcommunicates vacuum to the lower mold cavity 32 to draw the sheet P4into the lower mold cavity 36 via the suction forces. The timer contactsT4G (line L29) close and the clamp frame opening solenoid 91a (line L29)is energized. via the limit switch contacts LS-lla which were closedwhen the limit switch LS-ll was tripped by the lower platen 52 beingmoved to the raised position. When the clamp frame opening solenoid 91ais energized, the cylinder 91, at the forming station 14, is actuated toextend the piston 92 into the path of the limit switch LS-17 and closethe contacts LS-l7a (line L34) energizing the solenoid 26a (line L34)which actuates the clamp cylinders 26 on the sheet frame assembly 16supporting the plastic sheet P4. This releases the sheet P4 for downwardmovement with the lower mold 20. The lower mold 20 is lowered to thelowered position illustrated in chain lines in FIG. 4, when the timercontacts T4F (line L27) close to energize the solenoid 221; (line L26).

When the lower mold 20 is extended to the raised position, it also tripsthe frame supported limit switch LS-6 to close the limit switch contactsLS-6b (line L16) and energize, when the timer contacts T4D (line L17)close, the bottom heater oven control relay 2CR. As soon as the bottommold 20 is retracted, i.e., 10 seconds later, the limit switch LS-6 isdeactuated to open the contacts LS-6b and interrupt the relay 2CR (lineL16) so that the quartz heaters substantially provide flash heat only tothe light gauge sheet P2 at the second heating station 12. The heavygauge sheet P3 at the heating station 13 is heated by the heaters 15awhich are energized through the control relay 3CR (line L19) that isintermittently energized through the percentage timer control contactsT7A. Although the heaters 150 are intermittently turned on and off, theheating time is sufficient so that the temperature at the second station13 does not substantially fluctuate but rather, remains substantiallyconstant.

When the solenoid 22b (line L26) is energized and the lower mold 20carrying the sheet P4 has been lowered, as mentioned, the timer contactsT4A (line L5) close to energize the relay SCR (line L5) which closes thecontacts SCRl (line L3) to energize the rim lock solenoid 74a (line L4)and retract the rim lock arm 70. This actuates the limit switch LS-9,thereby closing the contacts LS-9a (line L33) to energize the turntablerotate solenoid 9A which indexes the turntable C and moves the sheet P3into the forming station 14 superposed with the now lowered sheet P4.When the turntable indexing rod 9' extends, the limit switch LS-l6 isactuated to open the contacts LS-16a and bleed the air pressure off theturntable indexing cylinder 9 so that the piston rod 9 does not abruptlyhalt, but coasts to its fully extended position.

When the turntable has been indexed the limit switchLS-4 is deactuatedand the limit switch LS-3 is tripped by one of the turntable supportedpaddles 76 (FIG. 1) to concurrently energize the timers T1, (line L8),T2 (line L9), T9 (line L9A), and T10 (line L10A). The lower mold 20temporarily dwells in the lowered position, and the upper platen 38 andupper mold 19 are lowered when the timer contacts T2A (line L23) closeto energize the top platen lowering solenoid 210 (line L23) whichdirects pressurized fluid to the cylinder 21 in such a manner as to movethe upper mold 19 to the molding position illustrated in FIG. 3. Thetimer contacts TlD (line L11) then close to energize the top vacuumcontrol solenoid 33a for introducing vacuum to the upper cavity 31 andmold 19 to form a shape in the sheet P3. At the same time, the timercontacts T2B (line L25) close to energize the lower platen, raisingsolenoid 22b which moves the lower platen 52 and the lower mold 20 tothe raised molding position so that the lower sheet P4 is engaged by thesuperposed sheet P3. At the time the sheets P4 and P3 are engaged, thelimit switches LS-S and LS-6 are tripped to close the limit switchcontacts LS-5a and LS-6a (line L6). When the lower mold 20 is moved toraised position, the lock shafts 43 and lugs 44 on the upper platen 38are received in head members 55 on the lower platen 52. When the timercontacts TlB (line L6) close, the platen lock solenoid 48a (line L6)will be energized to actuate the platen lock cylinder 48 and revolve theshafts 43 and the platen locks 44 90 to their locking positions receivedin the offset slot portions 55b. This provides a positive lock,positively preventing separation of the upper and lower platens 38 and52, respectively. The locking of the platens is signalled by theactuation of limit switch LS-7 which closes the limit switch contactsLS-7a (line L7). When the timer contacts TIC (line L7) close, thepressure squeeze solenoid 65a is energized to actuate the valve 65 whichcommunicates pressurized air to line 66 so that the hoses or expandableair bladders 63, on the lower platen 52, are expanded to the positionsillustrated in FIG. 6. This raises the lower mold 20 relative to theplatens and tightly squeezes the sheets P4 and P3 around their edges soas to pinch the sheets and reduce the combined thickness of the sheetsto about the thickness of the thinner gauge slieet P4. The upper andlower molds 19 and 20 remain in the operative positions until the formedobject cools. The molds l9 and 20 are then returned to their retractedpositions away from the part which is held by the carriage l6 clampingthe sheet P3 as will presently be described.

When the limit switch contacts LS-3a (line L4) close, the timers T9(line L9A) and T10 (line LlOA) are energized to close the contacts T9A(line L14) and T10A (line L16) to energize the heater oven controlrelays lCR (line L14) and 2CR (line L16) so that the sheet Pl which wasindexed to the first heating station or oven 11, is heated by the upperheaters 15 at the first oven 12. The sheet Pl, now at the first heatingstation 12, is a heavy gauge sheet so the contacts T9A (line L14) andTlOA (line L16) remain closed for a substantially longer period than thetimer contacts T4C (line L15) and T4D (line L17) were closed so that theheavier gauge sheet P1 will be heated by both upper and lower heaters 15for a relatively longer period of time than the lighter gauge sheet P2was previously heated by the second oven 12. The light gauge plasticsheet P2, which is now indexed to the second heating station [3, is alsoheated by the heaters 15a that are intermittently energized aspreviously described to maintain a substantially constant temperature atthe station 13.

More particularly, when the top platen 58 is extended, the timer T8(line L20) is energized to intermittently open and close the contactsT8A to energize the relay 4CR which selectively controls theencrgization of the lower heaters at the second oven 13. The temperatureat the oven or heating station 13 can be controlled by adjusting thetimer T7 and regulate the percentage of the timer operating time thatthe contacts T7A and T7B are closed. Although the heaters 15a at thesecond oven are intermittently energized. the heat does notsubstantially fluctuate. The lighter gauge sheets P2 and P4, which areflash heated only by the heaters 15 at the first heating station 12, areheated for a longer period of time by both top and bottom heaters at thesecond station 12.

A typical cycle time to complete the formation of the part at formingstation 14 is 4 minutes. Once the part has been assembled and thecarrier C is indexed, the operator at station 11 must unload thecompleted part and reload a heavier gauge sheet in 10 seconds. Thus,while the parts may typically be heated for 4 minutes. the two sheetswhich are assembled to make a part are in the heater units a total of 4minutes and 10 seconds. Neither will be heated during that entire lengthof time. The thinner gauge sheet obviously will be heated for a lesserperiod of time than the thicker gauge sheet. About 3 minutes heatingtime is required for the thicker gauge sheet, and about 2 minutesheatingtime is required for the thinner gauge sheet, and this isaccomplished by delaying the turning on of the quartz tubes 15 with thetimers T7 and T8.

When the turntable C was rotated to move the heavier gauge sheet P3 tothe forming station 14, the carriage 16, which previously supportedsheet P4, was moved to the load station 11 to actuate the limit switchLS-l3 and close the limit switch contacts LS-13a (line L30) to energizethe clamp frame opening solenoid 93a which actuates the unclamp cylinder93 at the loadunload station 11. This extends the piston 94 into thepath of the limit switch LS-l7 to close the limit switch contacts LS-17a(line L34). This energizes the solenoid 26A (line L34), causing theclamp frame assembly 16 previously supporting the sheet P4, to beopened. When the clamp frame assembly 16 is opened at the load station,the limit switch LS-2l (FIG. 2) is tripped to close the limit switchcontacts LS21a (line L33a) to energize the table raising solenoid 29a(line L33A) and move the sheet support table 27 upwardly to a positionin which the next sheet is received by the carriage previouslysupporting sheet P4. When it reaches the proper position, the limitswitch LS-12 is tripped to close limit switch contacts LS-l2a (line L31)and energize the solenoid 93b. This causes the piston rod 94 on thecylinder 93 to be retracted and deactuates the limit switch LS-17a sothat the clamp frame solenoid 26a (line L34) can be deenergized and theframe assembly 16 returned to its original clamping position.

After the sheets P4 and P3 are fused together and the hollow part isformed, the forming cycle is reversed and the timer contacts TIC (lineL7) open to deenergize the pressure-squeeze solenoid 84:: so that theair bladders 63 collapse. The timer contacts T1 (line L6) open todeenergize the platen lock solenoid 480 (line L6) permitting the platenlocking lugs 44 to be disposed in alignment with the keyhole slot 55a.Also, the timer contacts TlD (line L11) and T-lE (line L12) open todeenergize vacuum control relays 33a and 34a and remove the vacuum fromthe top and bottom molds. The timer contacts T2A (line L23) open todeenergize the upper platen lowering solenoid 21a permitting the uppermold 19 to be spring-returned to the raised position, and the contactsT2C (line L26) close to energize the lower mold lowering solenoid 22b.

The lower sheet P4 will be bonded to the upper sheet P3 to be carriedthereby in the clamp frame assembly holding the sheet P3. If necessary,conventional air ejection devices may be mounted on the topand bottommolds to assist in removing plastic sheets which inadvertently stick tothe molds. The top sheet with the part formed therein, separates fromthe top mold and the bottom sheet P4 separates from the bottom mold tobe carried by the clamp frame assembly holding the sheet P3.

With the part thus formed, the timer contacts TIA time out to energizethe rim lock retract solenoid 74a which retracts the rim lock 70 toactuate the limit switch LS-9. This closes the limit switch contactsLS-9A (line L33) and again energizes the turntable rotating solenoid 9A(line L33). This causes the turntable C to be indexed 90 so that theformed part is now disposed at the loading-unloading station. This willtrip the limit switch LS-l3 causing the contacts LS-13a (line L30) toagain close and energize the clamp frame opening solenoid 93a whichopens the clamp frame 16 supporting the part. The operator manuallyremoves the part and at the same time, the limit switch LS-21 is trippedto cause the next sheet on the turntable 27 to be raised into positionto be clamped by the clamp frame previously holding the sheet P3. Whenthe sheet reaches the raised position, the limit switch LS-12 is againtripped to close the contacts LS-12a (line L31) to energize the clampframe solenoid 93b and clamp the sheet on the carriage 16 to be indexedtherewith to the heating station 11. The cycle is then repeated. it isto be understood that the drawings and descriptive matter are in allcases to be interpreted as merely illustrative of the principles of theinvention, rather than as limiting the same in any way, since it iscontemplated that various changes may be made in various elements toachieve like results without departing from the spirit of the inventionor the scope of the appended claims.

I claim:

1. Apparatus for forming hollow thermoplastic objects from first andsecond thermoplastic sheets comprising:

a first and a second carriage means for releasably clamping respectivefirst and second thermoplastic sheets thereon,

indexing means supporting each of said first and second carriage meansfor step-by-step movement to a series of successive work stationsdisposed along an endless path with said first carriage means maintainedone step of movement in advance of said second carriage means, said workstations including a sheet transfer station, at least one heatingstation and a forming station.

a pair of opposed mold members mounted on opposite sides of said endlesspath at said forming station for movement between a normally maintainedspaced apart mold open position and a clampingly engaged mold closedposition,

means creating a sheet molding differential pressure in at least one ofsaid mold members,

first means operable upon the arrival of said first carriage means atsaid forming station for releasing a first sheet carried by said firstcarriage means from said first carriage means and transferring it to oneof said mold members. and for actuating said indexing means to advancesaid first carriage means from said forming station while simultaneouslyadvancing said second carriage means with a second sheet thereon to saidforming station,

second means operable upon the arrival of said second carriage means atsaid forming station to shift said mold members to said closed positionto fuse said sheets and thereby form said object while said second sheetis retained by said second carriage means,

and third means operable upon the formation of said object to restoresaid mold members to said open position and to actuate said indexingmeans to advance said second carriage means from said form ing stationwith the formed object supported thereon.

2. Apparatus as defined in claim 1 wherein said transfer stationcomprises a load-unload station and said first and second carriage meansare advanced successively from said forming station to said load-unloadstation, and loading means provided at said load-unload station operableto load a first sheet onto said first carriage means while said secondcarriage means is located at said forming station.

3. Apparatus as defined in claim 2 further comprising means foractuating said loading means to load a second sheet onto said secondcarriage means subsequent to the unloading of a formed object therefrom.

4. Apparatus as defined in claim 1 .wherein said first means comprisesfirst power means operable upon the arrival of said first carriage meansat said forming station for shifting said one mold member only from itsopen position into engagement with the first sheet on said firstcarriage means and responsive to the release of said first sheet fromsaid first carriage means to said one mold member for returning said onemold member to its open position with said first sheet.

5. Apparatus as defined in claim 1 wherein said second means comprisessecond power means operable upon the arrival of said second carriagemeans at said forming station for shifting said other mold member to itsmold closed position in engagement with the second sheet on said secondcarriage means, said differential pressure creating means forms saidsecond sheet to the conformation of said other mold member, and means isprovided for subsequently shifting said one mold member to its moldclosed position.

6. Apparatus as defined in claim 1 wherein said differential pressurecreating means conforms said first sheet to said first mold member priorto the arrival of said second carriage means at said forming station.

1. Apparatus for forming hollow thermoplastic objects from first andsecond thermoplastic sheets comprising: a first and a second carriagemeans for releasably clamping respective first and second thermoplasticsheets thereon, indexing means supporting each of said first and secondcarriage means for step-by-step movement to a series of successive workstations disposed along an endless path with said first carriage meansmaintained one step of movement in advance of said second carriagemeans, said work stations including a sheet transfer station, at leastone heating station and a forming station, a pair of opposed moldmembers mounted on opposite sides of said endless path at said formingstation for movement between a normally maintained spaced apart moldopen position and a clampingly engaged mold closed position, meanscreating a sheet molding differential pressure in at least one of saidmold members, first means operable upon the arrival of said firstcarriage means at said forming station for releasing a first sheetcarried by said first carriage means from said first carriage means andtransferring it to one of said mold members, and for actuating saidindexing means to advance said first carriage means from said formingstation while simultaneously advancing said second carriage means with asecond sheet thereon to said forming station, second means operable uponthe arrival of said second carriage means at said forming station toshift said mold members to said closed position to fuse said sheets Andthereby form said object while said second sheet is retained by saidsecond carriage means, and third means operable upon the formation ofsaid object to restore said mold members to said open position and toactuate said indexing means to advance said second carriage means fromsaid forming station with the formed object supported thereon. 2.Apparatus as defined in claim 1 wherein said transfer station comprisesa load-unload station and said first and second carriage means areadvanced successively from said forming station to said load-unloadstation, and loading means provided at said load-unload station operableto load a first sheet onto said first carriage means while said secondcarriage means is located at said forming station.
 3. Apparatus asdefined in claim 2 further comprising means for actuating said loadingmeans to load a second sheet onto said second carriage means subsequentto the unloading of a formed object therefrom.
 4. Apparatus as definedin claim 1 wherein said first means comprises first power means operableupon the arrival of said first carriage means at said forming stationfor shifting said one mold member only from its open position intoengagement with the first sheet on said first carriage means andresponsive to the release of said first sheet from said first carriagemeans to said one mold member for returning said one mold member to itsopen position with said first sheet.
 5. Apparatus as defined in claim 1wherein said second means comprises second power means operable upon thearrival of said second carriage means at said forming station forshifting said other mold member to its mold closed position inengagement with the second sheet on said second carriage means, saiddifferential pressure creating means forms said second sheet to theconformation of said other mold member, and means is provided forsubsequently shifting said one mold member to its mold closed position.6. Apparatus as defined in claim 1 wherein said differential pressurecreating means conforms said first sheet to said first mold member priorto the arrival of said second carriage means at said forming station.